First off, those are very, very thin rollers, 20mm is nothing. 20mm is about right for a mill jar 1/2 the diameter (1/4 the volume) of that jar. You need rollers at least 40mm - 50mm, especially the driving roller. If using heavy media your looking more towards 3".
I believe those milling jars are intended for spherical, lighter and harder ceramic media not steel media which is about 2 - 3 times more dense.
I think you have a mill mistaken for a modern day diesel powered car. The idea is that they are as noisy as humanly possible. The more noise the heavier the milling and the faster the job gets done. They only go quiet when they have powdered everything inside to a very fine,
free flowing powder and metals tend not to do this so your stuck with noise. Once way to eliminate the noise is to dig a f*ck off big hole in your garden, put the mill in it, then cover with a aggregate sack with 1/4 of a ton of damp mud in it. How could I possibly know this works???; because I made a mill for a 20L mill jar exactly like yours to mill Aluminium, we dug a hole like described and you had to listen hard to hear it @ 6m. That mill had 24mm hard silicone lined steel shafts, a close size to yours but we used ceramic media which is much lighter and still did the job. The jar was also lined with a softish rubber to gain a hundred times more traction.
Also from the picture of your mill I reckon you have all the ratios well far out. You should be looking for about 0.6 - 1.2 revolutions per second. To achieve that you would need to spin those drive shafts like their intended purpose. By the looks of it they do and that is most of your problem.
You need bigger rollers so that the ratio between the roller's revs and the jar's rev is as low as you can make it. By doing this you reduce the pressure exerted on the jar walls, this in tern prevents jar buckling. You also increase the traction area and reduce the sheer force required to spin the jar, this means your high friction material (of which there is none of on your machine) lasts longer. You can't spin a metal bar against a plastic jar really fast and expect anything useful to happen. The lower this ratio is the longer your jar lasts; direct drive (i.e. the ratio of 1:1) is one of the best possible solutions for a mill in this respect.
Your motor also does not look up to the job, you really need at least 1.5hp - 2hp to run a mill that size and heavy continuously without damaging either the mill, jar or motor. I'm just guessing but it looks more like 1/2hp.
You need: 1. More power.
2. Wider rollers.
3. Wear resistant roller surfaces with moderate tack.
(hard silicone tube for example)
4. High friction jar contact surfaces.
(typically softer as it needs to flex a little to gain traction area)
5. Lighter media for that particular jar.
6. Correct pulley ratios.
7. Sealed bearings.
(can't see yours but trust me you need them if you haven't already)
8. Generally time, money and know-how to build an effective mill that big.
9. Basically a proper well made mill.
I have a 3L mill that mills Aluminium perfectly well. Guess what the jar is; a PET cider bottle, to prevent jar buckling a modicum of liquid butane is added to the jar before sealing. The pressure remains at 4 bar no matter how much you add (the vapour pressure at standard temperature of butane), well below the yield pressure of the bottle. It is also a direct drive mill using a gearbox and has no driven rollers. One other way to mill Aluminium well is to get it really cold and then mill it.
The moral is, don't exceed your known empirical limits unless your prepared to research and fail a little. Also this has all been said many times before on this forum. And you don't need a massive mill.
Edited by Andrew, 18 April 2007 - 07:09 PM.
